This application claims the benefit of Japanese Patent Applications No. 2004-242803 filed Aug. 23, 2004 and 2005-168441 filed Jun. 8, 2005. The entire disclosure of the prior applications is hereby incorporated by reference herein in its entirety.
1. Technical Field
The present invention relates to an optical device, a projector and a manufacturing method of the optical device.
2. Related Art
Recently, there has been known a front projector that forms a projection image on a front side (a viewer side) of a screen for home use such as home theater system.
As for the front projector, a three-plate type has been known. The three-plate type separates a light beam irradiated by a light source lamp into three color lights of R, G and B by a color-separating optical system such as a dichroic mirror, modulates each separated light beam in accordance with image information with three optical modulators per each color light, forms an optical image by combining the light beams modulated by each optical modulator by a cross dichroic prism as a color-combining optical device, and projects the optical image by a projection optical device such as a projection lens in an enlarged manner.
The three-plate type projector employs an electro-optic device in which the three optical modulators are directly attached on light incident surfaces of the cross dichroic prism for simplifying the structure as well as the assembling step.
In the above electro-optic device, when the optical modulators are fixed on the light incident surfaces of the cross dichroic prism, the positions of the optical modulators need to be relatively adjusted to prevent an image quality from deteriorating due to pixel misalignment among the respective optical modulators. Owing to this, there is proposed a manufacturing method of the electro-optic device in which the three optical modulators are relatively adjusted for their positions and fixed on the light incident surfaces of the cross dichroic prism by a manufacturing apparatus (for example, see Reference: JP2002-244206A).
Specifically, provided on the manufacturing apparatus described in the above Reference are an adjustment screen, an optical axis detector and four image detectors. The color-separating optical device, the cross dichroic prism, the optical modulators and an optical component casing for housing the former components are combined to be the adjusting target.
As for the manufacturing method, a projection lens with typical optical characteristics is selected as a master lens, and attached on the manufacturing apparatus. Next, the adjusting target is set on the manufacturing apparatus, an illumination optical axis is detected by the optical axis detector, and the four image detectors are moved based on the detected illumination optical axis, for detecting four corners of a projection image. Then, the light beam irradiated by the light source lamp of the manufacturing apparatus is used for forming the projection image on the adjustment screen, so that the positions of the optical modulators are respectively adjusted while the four corners of the projection image being detected by the image detector. After the position adjustment, the optical modulators are respectively fixed on the cross dichroic prism.
As for the projector, in addition to the front projector, a rear projector have gradually been popular, in which a projection image is formed on a back side of a transmissive screen, so that a viewer views an image transmitted through the screen.
The rear projector includes an internal unit for projecting an optical image, a boxy casing for housing a reflection mirror etc. that reflects the optical image projected by the internal unit and the exposed transmissive screen provided in front of the casing. The internal unit includes a light source lamp, a color-separating optical device, optical modulators, a cross dichroic prism and a projection optical device similar to the front projector.
Accordingly, even in the rear projector, it is desired to employ the electro-optic device like that of the front projector for simplifying the structure as well as the assembling step, and also the rear projector is possibly manufactured by using a conventional apparatus in manufacturing.
Incidentally, in particular to the rear projector, since a transmissive screen and an image formation portion are housed in the casing, an aspect ratio of a projection image projected from the image formation portion is required to highly accurately be positioned on a projection surface of the transmissive screen. Therefore, when manufacturing the electro-optic device for the rear projector by the manufacturing apparatus described in the Reference, the four image detectors have to be positioned corresponding to the four corners of the projection surface of the transmissive screen highly accurately. If the four image detectors are positioned in the above-described manner, by relatively adjusting the positions of the optical modulators and thus manufacturing the electro-optic device so that the four corners of the projection image can be detected by the four image detectors, the aspect ratio of the projection image projected from the internal unit can highly accurately be positioned on the projection surface of the transmissive screen when the manufactured electro-optic device is assembled with the rear projector.
However, when the above-described manufacturing method is conducted, positioning of the four image detectors takes long time, and consequently the electro-optic device cannot be manufactured easily.
In the manufacturing method using the master lens, since there is existed deviation of the optical characteristics such as the position of the back focus between the projection lens and the master lens combined with the electro-optic device, the aspect ratio of the projection image projected by the internal unit cannot highly accurately be positioned on the projection surface of the transmissive screen depending on the projection lens to be combined even when the electro-optic device is manufactured by the above-described manufacturing method. Owing to this, when manufacturing the electro-optic device, since the manufacturing target needs to include the projection lens to be combined with the electro-optic device, the electro-optic device cannot be manufactured independently and effectively.